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Conversion of biomass and waste using highly preheated agents for materials and energy recovery
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology. (Energy and Furnace Technology)
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

One of the greatest challenges of human today is to provide the continuous and sustainable energy supply to the worldwide society. This shall be done while minimizing all the negative consequences of the operation(s) to the environment and its living habitants including human beings, taking from the whole life cycle perspective. In this thesis work new solutions for treatment biomass and waste are analyzed.

 

Based on the fundamental research on the conversion of various materials (biomass: straw pellets, wood pellets; and waste: plastic waste, ASR residues after pyrolysis), converted by means of different systems (pyrolysis in a fluidized bed reactor, gasification in a fixed-bed reactor using highly preheated agents) it is recommended to classify materials against their charring properties under pyrolysis, in order to find the best destination for a given type of fuel. 

 

Based on phenomenological research it was found that one of the important effects, affecting performance of downdraft gasifiers, is the pressure drop through the bed and grate. It affects, directly, the velocity profile, temperature distribution and of the height of the bed, especially for the grate with restricted passage surface, although it was not investigated in literature. The lower grate porosity, the higher conversion of fuel and heating value of gas is produced. However, the stability of the process is disturbed; therefore reducing the grate porosity below 20% is not recommended, unless the system is designed to overtake the consequences of the rising pressure inside the reactor. This work proposed the method for prediction of a total pressure drop through the fixed-bed downdraft gasifier equipped with a grate of certain porosity with an uncertainty of prediction ±7.10.  

 

Three systems have been proposed; one for the treatment of automotive shredder residue (ASR), one for the treatment of plastic waste (polyolefins) and one for biomass (wood/straw pellets). Pyrolysis is an attractive mean of conversion of non-charring materials (like plastic waste) into valuable hydrocarbons feedstock. It gives directly 15-30% gaseous olefins while the residue consisting of naphtha-like feedstock has to be reformed/upgraded to olefins or other chemicals (e.g. gasoline generation) using available petrochemical technologies. Pyrolysis of complex waste mixture such as ASR is an attractive waste pretreatment method before applying any further treatments, whereby useful products are generated (gaseous and liquid fuel) and char, rich in precious metals. The solid residues are meant for further treatment for energy and metals recovery. Gasification is a complementary method for handling pyrolysis residues. However, metals can be removed before gasification. Pyrolysis of charring materials, like biomass, is a very important step in thermo-chemical conversion. However, the char being approximately 25%wt. contains still very high caloric value of about 30MJ/kg. This in connection with the High Temperature Steam Gasification process is a very promising technology for biomass treatment, especially, above 900oC. This enhances the heat transfer towards the sample and accelerates kinetics of the gasification. This, in turn, improves the conversion of carbon to gas, increases the yield of the producer gas and reduces tar content. At higher steam to fuel ratio the process increases the yield of hydrogen, making it suitable for second-generation biofuels synthesis, whereas at lower steam to fuel ratio (S/F<2) the generated gas is of high calorific value making it suitable for power generation in a combined cycle.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , 115 p.
Keyword [en]
biomass, waste, pyrolysis, gasification, ASR
National Category
Metallurgy and Metallic Materials
Research subject
SRA - Energy
Identifiers
URN: urn:nbn:se:kth:diva-34253ISBN: ISBN 978-91-7501-033-5OAI: oai:DiVA.org:kth-34253DiVA: diva2:419864
Public defence
2011-06-15, D3 (entreplan), Lindstedtsvägen 5, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
StandUp
Note
QC 20110607Available from: 2011-06-07 Created: 2011-05-30 Last updated: 2011-12-12Bibliographically approved
List of papers
1. Pyrolysis of plastic waste for recovery of monomers and naphtha-like feedstock
Open this publication in new window or tab >>Pyrolysis of plastic waste for recovery of monomers and naphtha-like feedstock
(English)In: Journal of Waste ManagementArticle in journal (Other academic) Submitted
Abstract [en]

Pyrolysis of plastic waste is an alternative way of plastic recovery and could be a potential solution for the increasing stream of solid waste. The objective of this work was to increase the yield the gaseous olefins (monomers) as feedstock for polymerization process and to test the applicability of a commercial Ziegler-Natta (Z-N): TiCl4/MgCl2 for cracking a mixture of polyolefins consisted of 46 % wt. of LDPE, 30% wt. ofHDPE and 24 % of PP. Two sets of experiments have been carried out at 500oC and 650oC via catalyticpyrolysis (1% of Z-N catalyst) and at 650oC and 730oC via only-thermal pyrolysis. These experiments have been conducted in a lab-scale, fluidized quartz-bed reactor of a capacity of 1-3kg/h at Hamburg University. The results revealed a strong influence of temperature and presence of catalyst on the product distribution. The ratios of gas/liquid/solid mass fractions via thermal pyrolysis were: 36.9/48.4/15.7%wt. and 42.4/44.7/13.9%wt. at650oC and 730oC while via catalytic pyrolysis were: 6.5/89.0/4.5%wt. and 54.3/41.9/3.8%wt. at 500oC and 650oC, respectively. At 650oC the monomer generation increased by 55% up to 23.6 %wt. of total pyrolysis products distribution while the catalyst was added. Obtained yields of olefins were compared with the naphtha steam cracking process and other potentially attractive processes for feedstock generation. The concept of closed cycle material flow for polyolefins has been discussed, showing the potential benefits of feedstock recycling in a plastic waste management.

Keyword
Fluidized Bed, Pyrolysis, Feedstock Recycling, catalysts, plastic waste
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-34410 (URN)
Note
QS 2011 QS 20120326Available from: 2011-06-07 Created: 2011-06-07 Last updated: 2012-03-26Bibliographically approved
2. Conversion of Industrially Processed Biomass Waste into Value-added Products Using High Temperature Agents
Open this publication in new window or tab >>Conversion of Industrially Processed Biomass Waste into Value-added Products Using High Temperature Agents
2011 (English)In: International Conference on Thermal Treatment Technologies and Hazardous Waste Combustors, 2011Conference paper (Refereed)
Abstract [en]

Biomass can be utilized for energy and chemicals generation, gradually replacing the significance of fossil fuels. In this work the conversion of an industrially processed biomass waste (straw pellets) has been studied by means of High Temperature Steam Gasification (HTSG) and High Temperature Pyrolysis (HTP) at T=750-950oC and at three levels of steam to fuel ratio (S/F): 3.2; 1.875 and 0. The primary objectives are focused on a parametric study in which the emphasis is put on the influence of temperature and S/F on the reaction rate, conversion of carbon to gas, as well as yields, composition and heating value of generated Syngas. The results show the increasing trend in the reaction rate, hydrogen yield and tar cracking with an increase in agent temperature and S/F. However, this growth is significantly increased for the temperatures around 950oC. The yield of gas varied from 1.2 to 1.5 Nm3/kg for HTP to 1.5 to 2.5 Nm3/kg for HTSG and the LHV ranged between 8-13MJ/Nm3. At highest S/F the reduction of CO and hydrocarbons is observed even at 850oC yielding amount of hydrogen by 100% up to 38% compared with a lower S/F. Pyrolysis and lower S/F generated gas suitable for energetic purpose, whereas higher S/F for chemical synthesis.

National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-34417 (URN)2-s2.0-80051684077 (ScopusID)
Conference
International Conference on Thermal Treatment Technologies and Hazardous Waste Combustors (IT3/HWC), May 10-13, 2011, in Jacksonville, FL.
Note
QC 20110607Available from: 2011-06-07 Created: 2011-06-07 Last updated: 2011-06-07Bibliographically approved
3. Effect of Pressure Drop Due to Grate-Bed Resistance on the Performance of a Downdraft Gasifier
Open this publication in new window or tab >>Effect of Pressure Drop Due to Grate-Bed Resistance on the Performance of a Downdraft Gasifier
2011 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 25, no 11, 5366-5377 p.Article in journal (Refereed) Published
Abstract [en]

The grate-bed resistance coefficient appears to be an important operating parameter having a strong influence on the overall performance during downdraft fixed-bed gasification- it affects, directly, the velocity profile, temperature distribution, and height of the bed. To date no information on the pressure drop due to the grate-bed resistance has been found. The objective of this paper is to propose a correlation that can predict the total effectof pressure drop (caused by bed resistance and grate-bed resistance), through a grate of a certain surface porosity (open area/total area) covered by the porous bed. The term related to the grate-bed resistance is based on the effective grate porosity, which combined surface bed porosity with geometrical criteria of the grate. Based on this a new term has been integrated into the Ergun’s equation. The prediction has been validated within the experimental work conducted on a 0.7MW downdraft fixed-bed gasifier fueled with wood pellets. In this study, three grates of different porosities and thicknesses have been tested using various operating conditions. The predicted values of pressure drop showed a good agreement within the experimental results with ±7.10% of uncertainty. Although, the lower grate porosity, the higher conversion of fuel and heating value of gas is produced, the stability of the process is disturbed; therefore the grate porosity reduction below 20% is not recommended.

Keyword
Pressure drop, downdraft gasifier, fixed bed, grate resistance
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-34416 (URN)10.1021/ef201246c (DOI)000297001400049 ()2-s2.0-81555213086 (ScopusID)
Note
QC 20111212Available from: 2011-06-07 Created: 2011-06-07 Last updated: 2011-12-12Bibliographically approved
4. Recycling of automobile shredder residue with a microwave pyrolysis combined with high temperature steam gasification
Open this publication in new window or tab >>Recycling of automobile shredder residue with a microwave pyrolysis combined with high temperature steam gasification
2010 (English)In: Journal of Hazardous Materials, ISSN 0304-3894, E-ISSN 1873-3336, Vol. 182, no 1-3, 80-89 p.Article in journal (Refereed) Published
Abstract [en]

Presently, there is a growing need for handling automobile shredder residues - ASR or "car fluff". One of the most promising methods of treatment ASR is pyrolysis. Apart of obvious benefits of pyrolysis: energy and metals recovery, there is serious concern about the residues generated from that process needing to be recycled. Unfortunately, not much work has been reported providing a solution for treatment the wastes after pyrolysis. This work proposes a new system based on a two-staged process. The ASR was primarily treated by microwave pyrolysis and later the liquid and solid products become the feedstock for the high temperature gasification process. The system development is supported within experimental results conducted in a lab-scale, batch-type reactor at the Royal Institute of Technology (KTH). The heating rate, mass loss, gas composition, LHV and gas yield of producer gas vs. residence time are reported for the steam temperature of 1173K. The sample input was 10 g and the steam flow rate was 0.65 kg/h. The conversion reached 99% for liquids and 45-55% for solids, dependently from the fraction. The H-2:CO mol/mol ratio varied from 1.72 solids and 1.4 for liquid, respectively. The average LHV of generated gas was 15.8 MJ/N m(3) for liquids and 15 MJ/N m(3) for solids fuels.

Keyword
ASR, High temperature steam gasification, HTAG, Microwave pyrolysis
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-26659 (URN)10.1016/j.jhazmat.2010.05.140 (DOI)000282240800011 ()2-s2.0-77955574707 (ScopusID)
Note
QC 20101202Available from: 2010-12-02 Created: 2010-11-26 Last updated: 2011-06-07Bibliographically approved
5. Conversion of microwave pyrolysed ASR's char using high temperature agents
Open this publication in new window or tab >>Conversion of microwave pyrolysed ASR's char using high temperature agents
2011 (English)In: Journal of Hazardous Materials, ISSN 0304-3894, E-ISSN 1873-3336, Vol. 185, no 1, 472-481 p.Article in journal (Refereed) Published
Abstract [en]

Pyrolysis enables to recover metals and organic feedstock from waste conglomerates such as: automotive shredder residue (ASR). ASR as well as its pyrolysis solid products, is a morphologically and chemically varied mixture, containing mineral materials, including hazardous heavy metals. The aim of the work is to generate fundamental knowledge on the conversion of the organic residues of the solid products after ASR's microwave pyrolysis, treated at various temperatures and with two different types of gasifying agent: pure steam or 3% (v/v) of oxygen. The research is conducted using a lab-scale, plug-flow gasifier, with an integrated scale for analysing mass loss changes over time of experiment, serving as macro TG at 950, 850 and 760 degrees C. The reaction rate of char decomposition was investigated, based on carbon conversion during gasification and pyrolysis stage. It was found in both fractions that char conversion rate decreases with the rise of external gas temperature, regardless of the gasifying agent. No significant differences between the reaction rates undergoing with steam and oxygen for char decomposition has been observed. This abnormal char behaviour might have been caused by the inhibiting effects of ash, especially alkali metals on char activity or due to deformation of char structure during microwave heating.

Keyword
ASR char, Microwave pyrolysis, High temperature agent gasification, Pyrolysis rate, Gasification rate
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-33712 (URN)10.1016/j.jhazmat.2010.09.056 (DOI)000289446700064 ()2-s2.0-78649332755 (ScopusID)
Note
QC 20110520Available from: 2011-05-20 Created: 2011-05-16 Last updated: 2011-06-07Bibliographically approved

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